One known type of information storage device is a disk drive unit that uses magnetic media to store data and a movable read/write head that is positioned over the magnetic media to selectively read from or write to the rotating magnetic media, such as magnetic disks.
FIG. 1a illustrates a conventional disk drive unit 100 and show a magnetic disk 104 mounted on a spindle motor 105 for spinning the disk 104. A head stack assembly (hereinafter referred as to HSA) 102 carries a slider 101 incorporating a read/write head. A voice-coil motor (VCM)103 is provided for controlling the motion of the HSA 102 and, in turn, controlling the slider 101 to move from track to track across the surface of the disk 104, thereby enabling the read/write head to read data from or write data to the disk 104. In operation, a lift force is generated by the aerodynamic interaction between the slider 101 and the disk 104. The lift force is opposed and balanced such that a predetermined flying height above the surface of the spinning disk 104 is maintained over a full radial stroke of the HSA 102. Also provided is a load/unload mechanism 106, which usually is embodied as a ramp to load/unload the slider 101 therefrom. In addition, all above components are disposed in an enclosure 122.
FIGS. 1b-c show in more detail the HSA of the disk drive unit of FIG. 1a. As depicted in the drawings, the HSA 102 comprises a drive arm 109 which has a mounting hole defined in its proximal end and which has a slider 101 disposed at its distal end, a fantail spacer 108 having a through hole defined therein, and a pivot bearing assembly to interconnect the drive arm 109 and the fantail spacer 108. The HSA 102 may further have a flex print circuit board assembly (FPCBA) 150 coupled to the remainder of the HSA 102 via a flex cable 110 so as electrically connect the HSA 102 with an external control device.
The pivot bearing assembly 107 comprises a pivot bearing 107a with a flange 191 extended radially from outer circumferential surface thereof, a washer 107b and a screw nut 107c, both of which are used cooperatively for securing the drive arm 109 and the fantail spacer 108 together. In assembling process of the HSA 102, first, the pivot bearing 107a passes through the mounting hole 111 of the drive arm 109 and the through hole 112 of the fantail spacer 108 such that end surface of the drive arm 109 is pressed forcibly against the flange 191 and the fantail spacer 108 is securely pressed against the drive arm 109. Then, the washer 107b and screw nut 107c are employed to fasten the drive arm 109 and fantail spacer 108 onto the pivot bearing 107a. 
However, manufacturing cost of this type of HSA is inherently increased as additional components, i.e., a washer and screw nut are inevitably used for mounting purpose. Besides, as additional components are used in assembly process, assembly process is complicated and time-consumed.
Thus, it is desired to provide a novel HSA which overcomes drawbacks of prior art.